Monthly Climate Statement for May 2014

The Science Division of the Department of Science, Information Technology, Innovation and the Arts (DSITIA) considers that there is a slightly higher than normal probability of exceeding median rainfall over the next three-month period (May to July) for most of Queensland. This view is based on DSITIA’s analysis of the historical relationship between Queensland rainfall and the Southern Oscillation Index (SOI) which, at this time of year, is weak. Furthermore, and with much higher confidence, the probability of a wet summer (November to March 2014/15) is very low based on DSITIA’s analysis of the current extra-tropical Pacific Ocean sea surface temperature (SST) pattern. Read more (PDF, 134K, last updated 12:05PM, 15 May 2014)*

DSITIA’s rainfall outlooks for Queensland are based on the current and projected state of the El Niño-Southern Oscillation (ENSO) phenomenon and on factors which alter the impact of ENSO on Queensland rainfall (i.e. the more slowly changing extra-tropical SST pattern in the Pacific Ocean).

At this time of year (known as the ‘autumn predictability gap’), the ENSO pattern tends to change very rapidly. Although the change in the ENSO pattern over autumn may provide a guide as to the likely development of an El Niño or La Niña event, it will not be until June that the prevailing ENSO pattern (as measured by indices such as the SOI or central equatorial Pacific Ocean SST anomalies) will provide a more useful basis for seasonal forecasting (i.e. for providing rainfall outlooks for winter, spring or summer).

However, DSITIA scientists have shown that extra-tropical SST anomalies, when measured in specific regions of the Pacific Ocean at this time of year, do provide a useful basis for long-lead forecasting of summer rainfall in Queensland. This information has been incorporated in an experimental system known as SPOTA-1 (Seasonal Pacific Ocean Temperature Analysis version 1), which has been operationally evaluated by DSITIA scientists for over a decade. 

The El Niño - Southern Oscillation (ENSO)

While it is useful to monitor the change in ENSO indices over this time of year as a guide as to whether an El Niño or La Niña pattern may develop, the prevailing ENSO pattern (as measured by indices such as the SOI or central equatorial Pacific Ocean SST anomalies) over coming months will provide a more useful basis for providing seasonal outlooks for winter, spring and summer.

Currently:

  • The SOI, a key-atmospheric measure of ENSO, rose sharply from -12.0 in March to +6.4 in April. The three-month mean SOI value from February to April was -2.4, remaining in the ENSO-neutral range.
    •  
  • Observed SST anomalies in the key Niño 3.4 region of the central equatorial Pacific Ocean warmed by 0.46 ºC from March (-0.22 ºC) to April (+0.24 ºC). The latest weekly SST anomaly (+0.5 ºC as at 10 May) has shown further warming.
    •  
  • Most international global climate models currently indicate that central equatorial Pacific Ocean SSTs should continue to warm in the coming months, with a greater than 75 per cent probability of El Niño conditions developing. 

What if an El Niño develops this year?

Currently, 80 per cent of Queensland remains drought declared under State Government processes, with shire and part-shire declarations remaining unchanged since March 1, 2014. While patchy rainfall during February, March and April has brought relief to some drought affected regions, the probability of an El Niño event developing over winter, and with it the threat of another dry summer for some regions, poses a risk of current drought conditions becoming more protracted. This risk should be factored into decision making and allocation of resources. In this context, it should be noted that:

  • The current long-lead outlook is based solely on extra-tropical Pacific Ocean SST anomalies and does not yet factor in central equatorial Pacific Ocean SST anomalies which, in coming months, will define the state of ENSO (‘El Niño’, ‘La Niña’ or ‘ENSO-neutral’) for 2014/15.
    •  
  • SST anomalies are approaching El Niño thresholds in the central equatorial Pacific Ocean, with a growing body of evidence pointing to the likely development of an El Niño pattern in coming months. The Bureau of Meteorology, in their latest ‘ENSO Wrap-Up’ (PDF)* (issued May 6), note that ‘El Niño development is possible as early as July’.
    •  
  • Should an El Niño event occur, this coupled oceanic and atmospheric pattern would likely persist over the coming summer (November to March).
    •  
  • An El Niño pattern in the central equatorial Pacific Ocean, coupled with the current extra-tropical Pacific Ocean SST pattern, would weaken the atmospheric Walker Circulation, leading to a high probability of dry conditions (< decile 3 rainfall) for much of Queensland over the coming summer.
    •  
  •  Irrespective of how ENSO develops, the probability of wet conditions (> decile 7 rainfall) for much of Queensland will remain low over the coming summer.
    •  
  •  DSITIA’s long-lead outlook for summer rainfall will be reassessed in June, and then updated monthly until November, by factoring in the most recent ENSO conditions.

* Requires Adobe Reader

Last updated: 30 March 2018
Creative Commons Attribution 4.0 International (CC BY 4.0)